1. Field of the Invention
The present invention relates generally to methods and apparatus for securing medical devices and more particularly methods and apparatus for securing medical devices such as parenchymal catheters or electrical stimulation leads within a cranial burr hole.
2. Description of the Related Art
Medical procedures involving access to the brain through a burr hole in the skull are under increasing use. Two such procedures are electrical stimulation of the brain for such purposes as relief of chronic pain and treatment of movement disorders, and the use of parenchymal catheters for infusing pharmaceutical agents. A typical electrical brain stimulation system comprises a pulse generator operatively connected to the brain by a lead having at its distal end an electrode designed to be implanted within the brain, and having at its proximal end a connector assembly designed to connect to the pulse generator. Use of a parenchymal catheter generally involves the insertion of a catheter within the brain to dispense pharmaceutical agents at a specific desired location.
One critical aspect of the above-listed procedures, and of any other such procedures that involve instrument access to the brain through a burr hole, is the precision with which any such inserted devices, e.g. catheters and leads, are placed. Once a satisfactory burr hole is established at a particular site, to avoid unintended injury to the brain, physicians typically use stereotactic procedures to position the inserted devices. One stereotactic instrument which may be used, for example, to position a lead electrode is disclosed in U.S. Pat. No. 4,350,159 to Gouda, incorporated herein by reference. As can be appreciated, once an inserted device is properly positioned, it is important that the device not be moved. Even one millimeter of travel of the positioned device may cause unsatisfactory results or, in some cases, severe injury to the brain. Accordingly, reliable methods and apparatus for fixing the positioned device at the burr hole are necessary.
Previous designs of systems for securing a positioned device within a burr hole have a number of drawbacks. U.S. Pat. No. 4,328,813 to Ray, incorporated herein by reference, discloses a socket and cap arrangement in which the cap is positioned so as to trap a positioned electrical stimulation lead between the socket and cap by friction. That arrangement involves securing the lead off center from the burr hole in a manner such that during installation of the anchoring cap the lead is secured in place. The lead, however, often needs to be manually supported in place while the anchoring cap is being installed. The lead is thus susceptible to inadvertent movement by the physician during the cap installation period. Further, in the interaction of the cap and socket, the lip of the cap tends to pull on the lead and to cause its dislodgement.
Previous systems also are susceptible to leakage of cerebrospinal fluid (CSF) during the operating procedure to implant the burr ring and lead or catheter. The present invention is directed to overcoming the disadvantages of the foregoing systems.